Dr Jekyll
The correct height for any individual in any military cockpit fitted with a HUD is that which makes their eye line level with the centre of the HUD display.
Known as the 'eye datum' this eye position is what the whole cockpit layout is designed around. This is actually lower than most people would like to sit from a simple external view point of view, which is of course at its best when your helmet is almost touching the canopy.
With everybody's eye at the eye datum height then canopy to helmet clearance is clearly not affected by individual height or sitting height. Although cone-heads may have a problem.
The seat was obviously fully up when you were in it - what a pity you did not ask your guide how to lower it.
